Yes, and you could do it two ways. Dig into Contact Form 7’s code, and hard-code it there.

Or you could do it with Javascript alone, which would be entirely independent of Contact Form 7’s code. I like using this method when working on systems where the infrastructure makes it impossible or wretchedly difficult to get into the system code (like Joomla, for instance). So for instance, you could write validation code that sits on top of the site, so to speak.

But is there an instant way to do this? No. Some Javascript coding ability required.